How to filter list elements starting with a given prefix using Python?

The word prefix is ​​defined by the beginning of a word or letter. In this article, we will learn how to filter list elements starting with a given prefix using Python using Python built-in functions like startswith(), filter(), lambda, and len().

Let us take an example to understand this problem−

Let’s take an example to understand this:
Given element list, My_list = [“Amelia”,  “Kinshuk”,  “Rosy”,  “Aman”]
Keyword to be searched, Prefix = “Am”
Final result = [“Amelia”, “Aman”]

grammar

The following syntax is used in all examples -

startswith()

This is a built-in method in Python that returns true if the given condition is met and the string starts with a specific value.

filter()

The filter() method is applied when we need to filter items based on specific conditions. Simply put, it allows the user to iterate over those elements that satisfy a condition.

lambda

This lambda function in Python is called an anonymous function. It can be used when a function object is required.

len()

This is a built-in method in Python that returns the length of the item in the object.

Use list comprehension

This program uses a list comprehension with a method called startswith() to filter the prefixed elements in the list.

Example

Example

In the following example, we will use a list comprehension in the return statement of a function named prefix_list_element_filter() which will iterate over the list values ​​using a for loop and startswith ()Check prefix. The combination of a for loop and an if statement in the same position is called a list comprehension. Then create the list in the variable my_list. Continuing with the setup of the calling function, pass the parameters my_list (stored list value) and Am (prefix) to filter list elements that start with the given prefix. Finally, we use the variable filter_list to print the results.

def prefix_list_element_filter(lst, prefix):
   return [item for item in lst if item.startswith(prefix)]

# Create the list
my_list = ["Amar", "Bunny", "Aman", "Ganesh", "Rajendra"]
filter_list = prefix_list_element_filter(my_list, "Am")
print("The given element start with prefix:", filter_list)

Output

 The given element start with prefix: ['Amar', 'Aman']

Use for loop

The program uses a for loop to iterate over the given list and checks the prefix using startswith(). It will then use an empty list to store the filtered prefix elements by using a built-in method called append().

Example

Example

In the following example, we first start the program by defining a function using the def keyword, which accepts two parameters - lst (for receiving list values) and prefix (for receiving prefix keywords). Next, it will iterate over the list using a for loop and then set the prefix using the startswith() method, which accepts the parameter prefix value received by the function. The filtered list elements are then added to the variable filtered_list using a method called append() and the result is returned. Now create the list in variable fruit_list. Then use the call function to pass the list value and prefix parameters into the variable filter_list. Finally, the results are printed using a variable named filter_list.

def prefix_list_element_filter(lst, prefix):
   filtered_list = []
   for item in lst:
      if item.startswith(prefix):
         filtered_list.append(item)
   return filtered_list

# Create the list
fruit_list = ["apple", "banana", "avocado", "blue berry", "kiwi"]
filter_list = prefix_list_element_filter(fruit_list, "b")
print("The given element start with prefix:\n", filter_list)

Output

 The given element start with prefix:
 ['banana', 'blue berry']

Use Filter() function

The program uses the filter() function to identify specific prefixes and uses the lambda function to set the prefix through a method called startswith(), which can be used to filter specific prefixes.

Example

Example

In the following example, a function starting with the def keyword is used, which accepts two parameters - lst (receives a list value) and prefix (receives a specific keyword search), this function will filter the list of items based on whether they start with a given prefix. This function returns a prefixed result. Then create a list to store the string values ​​in variable course_list. Next, use a function call to pass the values ​​- pass course_list and "bc" in the variables filter_list. Now use the print function setting the variable name filter_list to get the results.

def prefix_list_element_filter(lst, prefix):
   return list(filter(lambda item: item.startswith(prefix), lst))

# Create the list
course_list = ["dca", "bca", "bcom", "MCA", "pgdca"]
filter_list = prefix_list_element_filter(course_list, "bc")
print("The given element start with prefix:\n", filter_list)

 The given element start with prefix:
 ['bca', 'bcom']

Example

In the following example, start using the function

, which accepts two parameters -

(to store the list) and

(in the function receive a specific prefix during the call). This function returns a new list by using a list comprehension, i.e. the expression item[:len(prefix)] slices the length of each item in lst from the beginning to the prefix and compares it with the prefix. If they are equal, include the item in the new list. Next, create a list to store some string values ​​in the variable

. Then initialize the variable filter_list, which has the same name as the above function, to pass the values ​​of the list and prefix. Finally, use the variable filter_list to get the results in the print function.

def filter_list_elements_prefix(lst, prefix):
   return [item for item in lst if item[:len(prefix)] == prefix]

# Create the list
my_list = ["tea", "coffee", "cheese", "teaspoon", "sugar"]
filter_list = filter_list_elements_prefix(my_list, "tea")
print("The given element start with prefix:\n", filter_list)

 The given element start with prefix:
 ['tea', 'teaspoon']